New dates on the impact shows it finished off what volcanic eruptions started.

Of all the mass extinction events in Earth’s history, the most familiar is probably the one that wiped out the dinosaurs and ushered in the age of the mammals. Most of us know the story—a hellish meteor impact that dragged about 3 out of every 4 species into extinction.

But the story is more complicated than that. There was also a series of incredibly massive and long-lived volcanic eruptions—they formed the Deccan Traps—around the same time. A second smoking gun, if you will. So which one did in the dinosaurs? Well, that depends on when the bullets were fired.

The debate started with the discovery of a layer of clay present throughout the world, and situated right at the boundary of the Cretaceous and (more recent) Paleocene rocks, marking the point where the fossils suddenly change. In the clay, there was a curiously sharp spike in iridium—an element that is generally rare in Earth’s crust. That suggested an extraterrestrial visitor (of the rocky and violent kind), since some asteroids are rich in elements like iridium.

Later, the Chicxulub Crater just off the Yucatán Peninsula was found to be of about the right age. But attempts to date the crater, the Deccan Traps, and the iridium-rich clay led to conflicting results. Some estimates put the meteor impact several hundred thousand years before the extinction event. Others showed the impact arriving after the extinction.

But puzzled dinosaur lovers need not fret, as a new study using improved dating methods has found that the meteor impact lines up nicely with the extinction after all.

The confusion arose from the error bars for dates this old (66 million years) being too large to reliably work out the details on the scale of a few tens of thousands of years, details that were important to this story. A recent refinement of a method for determining the age of certain types of rock (one based on the decay of potassium into argon) made it possible to more accurately and precisely date the extinction.

The age of the impact that created the Chicxulub Crater was pinned down using tiny blobs of rock that were ejected white-hot from the impact crater, cooled mid-air, and landed (in this case) in Haiti. The age for the extinction came from layers of (local) volcanic ash near the iridium-rich clay at a site in Montana. As confirmation, some of the ash was also dated using the decay of uranium to lead, as well.

The dates for the impact and extinction were essentially identical, within the error bars of about 30,000 years—or as Paul Renne, a UC-Berkeley professor who led the study, explained in a university press release, “We have shown that these events are synchronous to within a gnat’s eyebrow.”

The timeline the study sets out includes drastic climate changes in the million years before the meteor hit. As the Deccan Traps eruptions sputtered to life, their emissions drove several sharp drops in global temperature. After millions of years of a hot climate, these cooler periods were likely rough for many species. It was during this already difficult time that the meteor struck the killing blow.

A more detailed account of the Deccan Traps will be needed to establish this version of events, but this work represents significant progress towards fleshing out the demise of the dinosaurs.

The new dates also shorten up the time between the extinction and the return of vertebrate fossils (including mammals) in the Montana rocks. What had previously been thought to be a 400,000 year hiatus now appears to have been less than 50,000 years. Given that short timeframe, the creatures that show up in these fossils were probably survivors from other regions rather than new species that arose after the extinction cleared the ecological decks—preparing the way for the mammal revolution.

So basically, the Dinosaurs were already going through some significant ecological challenges from the global cooling. Would this already have provided an advantage to Mammals? Then came the straw to break the camel's back and unleash the Mammals.

As far my recollections is also a lack of plant or any other kind of growth for hundreds of thousands of years after the astroid. Which why the layer is so distinct, and not indicative of a common meteor strike. After a meteor strike, things get bad for a few years then back to normal with a small upset. 50,000 years changes much it seems a bit revisionist (what does it change?) as far as I remember this extreme hardship lasted for hundreds of thousands of years after and hundreds of thousands of years before and was a very tough time. Most of the very harsh stuff was in the East by India, the west was where things were somewhat better. Then a giant astroid, that was not it's not that remarkable in size, but a ideal western location to harm what was left in a very tough time. After the astroid hit life wasn't getting better and life had a very tough time for any comeback. Especially any large animals where the food resources per square foot had been reduced significantly.

I'm having a little difficulty with the article, but I read it as implying that the Deccan Trap definitely began erupting before Chicxulub hit; the analysis demonstrating that the extinctions don't begin in earnest at that time, but onlyafter Chicxulub. Is that correct?

If so, a shame (for me). My favorite pet theory was that the Deccan Traps were caused by Chicxulub: this made sense to me because they are almost exactly on the other side of the planet (and for all I knew, might have been exactly at the other side at that time). I imagined them being the result of the Chicxulub shockwaves meeting.

A show I saw on the Science Channel a couple years back touched on this. There is some debate on whether a meteor was what pushed them to extinction. There's evidence that the climate was changing in a direction that was not favorable to them before the arrival of the 1 or 2 meteors that hit the planet. Yes there's debate also over if it was just one major strike or if there were 2.

I wonder if the Deccan Traps and the meteor could be linked? Maybe that meteor got captured by the Earth for a few thousand years prior to the impact? It might have done close passes which disturbed the Earth's orbit or maybe dropped small pieces which punched holes (creating the Traps?). Then the main body finally got twisted so that it hit the Earth.

While it is a nice study, the reality is that we've never found non-reworked non-avian dinosaur bones above the boundary marked by the impact. More confirmation is always nice, but its been known for a while, and it was pretty blazingly clear. Some people don't -like- the idea that an impact killed them off, but the evidence has been pretty incontrovertible.

If so, a shame (for me). My favorite pet theory was that the Deccan Traps were caused by Chicxulub: this made sense to me because they are almost exactly on the other side of the planet (and for all I knew, might have been exactly at the other side at that time). I imagined them being the result of the Chicxulub shockwaves meeting.

I always liked that one too; unfortunately sometimes correlation is only a coincidence.

If this were true there wouldn't be any debate going on in scientific circles about this. this sounds an awful lot like the nonexistent 'consensus' on climate change.

Uh, not really. Climate change is accepted by virtually all climatologists, just as the impact theory has been accepted by virtually all paleontologists. There have been holdouts because a lot of scientists hate catastrophism; however, the position that the Deccan Traps caused it is in direct conflict with the fossil record, as the traps started erupting prior to the extinction event, and yet the extinction is clearly marked by the iridium layer from a major impact event. Some complain that there were other factors which might have contributed, and its probably true that they DID contribute, but the impact marked a very clear boundary so the idea that it wasn't the primary cause is rather silly - the change is marked, and marks the KT (well, K-Pg now) boundary clearly. Indeed, it defines the boundary.

If this were true there wouldn't be any debate going on in scientific circles about this. this sounds an awful lot like the nonexistent 'consensus' on climate change. Just because a theory has been popular for a very long time does not make it correct. Scientific theories are adjusted as more and better data is made available.

Consensus is not nonexistent on climate change. Don't confuse debate over the details, which as you said, always happens in science, with debate over the large scale idea, of which there is very little among climate scientists.

Your comparison to climate change is more like saying there is debate over whether the extinction occurred at all, rather than debate over the details of exactly how it happened.

Quite interesting. We already have proof that major volcanic activity can disrupt the global ecosystem from the formation of the Siberian Traps 250 million year ago (in which 90-95% of all species were wiped out, including marine life), so it was not as far fetched as might be imagined. Granted, the Deccan Trap formation was a much smaller event (relatively), but I would think that, should it have occurred before the meteor, it's effect would be too great to overlook. As a whole, dinosaurs do not seem adaptable to rapid environmental shifts, and I think they would have already been suffering before the meteor strike, which was the killing blow.

Perhaps it is just me in reading this article, but it looks like they haven't ruled out the Deccan Trap formation occuring before the meteor, it has just settled that the meteor was the final blow. Personally, I still think the Deccan Traps were significant, so long as they nail the date down before the meteor. If it was after the extinction event, well, perhaps it simply solidified the rise of the more adaptable mammals.

(for reference:)

Lava coverage area: 500,000 km2 (Deccan) vs 7,000,000 km2 (Siberian), with the final formations being roughly 50% thicker and about 8 times the lava in the case of Siberian. So vastly larger, but I would think the Deccan would apply environmental pressure regardless. We're still talking about a vastly larger eruption than anything experienced in the relatively recent geologic timescale)

If this were true there wouldn't be any debate going on in scientific circles about this. this sounds an awful lot like the nonexistent 'consensus' on climate change.

Uh, not really. Climate change is accepted by virtually all climatologists, just as the impact theory has been accepted by virtually all paleontologists. There have been holdouts because a lot of scientists hate catastrophism; however, the position that the Deccan Traps caused it is in direct conflict with the fossil record, as the traps started erupting prior to the extinction event, and yet the extinction is clearly marked by the iridium layer from a major impact event. Some complain that there were other factors which might have contributed, and its probably true that they DID contribute, but the impact marked a very clear boundary so the idea that it wasn't the primary cause is rather silly - the change is marked, and marks the KT (well, K-Pg now) boundary clearly. Indeed, it defines the boundary.

Your assurity seems a little off. If you look at the clay formations with the irridium layer, both before and after the Iridium layer is a dead zone. It is not that catastrophism is fought against, but it doesn't make sense by itself as there have been thousands of others the same size or bigger hit the earth with very little change in the earth or the life on it. So what makes this special, which is where the debate is. There are far fewer dinos coming up to the KT boundary. In fact until recently there hadn't been one found. They were under serious pressure with decrease food/area for the larger dinos, the last holdouts were most likely in the west away from the traps, which is where the closest to the KT boundary dino bones were found.

So if the KT boundary is so absolute and striking. Why doesn't life just go on from there like all the other impacts?

Is it? Nice try. No one is debating the reality of the extinction of the dinosaurs. What's at issue here is the method.

Just like how NO ONE who knows he science is saying climate change isn't happening. That's the nature of our climate system. It's DYNAMIC. It's always in a state of change. What's at issue in THAT debate isn't whether or not the climate is changing. Researchers are debating over what are the factors driving the on going changes.

I was only responding to your post about how there is no consensus on climate change. You didn't say there is no consensus on anthropogenic climate change. That was exactly my point, very few are now arguing the climate isn't warming, just like no one is arguing the dinosaurs didn't go extinct. It's obvious, and mostly beyond debate to anyone not willfully blind to the science.

I'll grant that there is still debate over the exact contributions of various causes, but I think you over estimate the amount of debate about whether a large part of those are due to human activity, regardless of the exact percentage.

Your comparison to climate change is more like saying there is debate over whether the extinction occurred at all, rather than debate over the details of exactly how it happened.

EDIT: Beaten by Titanium Dragon

Is it? Nice try. No one is debating the reality of the extinction of the dinosaurs. What's at issue here is the method.

Technically, coelurosaurs are still going strong (being the most diverse vertebrate branches today).

True enough. If the theory that birds evolved from dinosaurs is correct then it's clear that not all dinosaurs died out. Enough survived long enough to evolve into birds.

This area of research reminds me of the debate over the fall of Rome. You have the historians who feel Rome never fell it just changed and the others who argue that Rome indeed did fall.

There were many dino proto-birds before the KT, there are many branches of dino birds that died off at the extinction leaving just one that made it through, although there is some debate whether one offshoot also made it for a time. The difficulty is it is hard to discern which branch some of them were in by a few bones.

[The Deccan Trap] flows are interrupted by intermediate layers of sedimentary rocks, indicating that the volcanic activity that shook and remodelled the area from about 68 million years ago was not continuous. It was also not catastrophic; fossils found in the sedimentary layers suggest that dinosaurs had coexisted with this activity reasonably well.

There doesn't seem to be a direct connection suggested, but similar formations in Siberia were linked to an impact in Antarctica in Science

Applogies if the fancy stuff in this post doesn't work, Preview doesn't work in my current environment.

I plugged in some numbers for something of the size of the K/T impactor (15km diameter, 20km/s speed, 90 degree angle, dense rock composition) and in 1000km distance (about 621 miles for you non-metric people out there) you'll get this: First, you will get 3rd degree burns from the fireball/thermal radiation of the impact, second, shaken by a magnitude >10 earthquake, and, third, hit by the shockwave/air blast coming at you with a speed of 342 m/s (766 mph). Everything at this location will be covered by about a meter of ejecta from the impact.

Don't forget that the impact site is in the ocean and Tsunamis will be generated. Also, immense Hurricanes could be generated over the impact site.

Go play with the calculator and you could find out what it takes to destroy earth

While it is a nice study, the reality is that we've never found non-reworked non-avian dinosaur bones above the boundary marked by the impact. More confirmation is always nice, but its been known for a while, and it was pretty blazingly clear. Some people don't -like- the idea that an impact killed them off, but the evidence has been pretty incontrovertible.

If this were true there wouldn't be any debate going on in scientific circles about this. this sounds an awful lot like the nonexistent 'consensus' on climate change. Just because a theory has been popular for a very long time does not make it correct. Scientific theories are adjusted as more and better data is made available.

For a theory that's only 30 years old, it's in pretty good shape. You're right that consensus doesn't mean squat - what matters are the data.

At first it was just the iridium spike in the Gubbio rocks that pointed to an asteroid and plankton size change spanning the KT boundary. Then the volcano group said that iridium is found in some volcano outgassing so perhaps the volcanos did the dinosaurs in. Then someone found a similar iridium-laced sequence in the Netherlands. And then an iridium KT sequence showed up in Spain. Then the meteor group found that all the KT iridium was laced with an isotope that isn't terrestial. Then they found a crater. But the crater was in water which was weird because the KT clays all suggested a land-based crater. Then they found tsunami evidence. Then they found that tektite distribution patterns that were consistent with a Coriolis distribution. The tektites helped tighten down the dating. Then someone figured out that the debris generated by the Chixilub geology would mimic a land-based crater not an aquatic crater.

Throughout the entire process, the meteor group kept pointing out that no one had found dinosaur remains younger than the KT boundary. When someone found what they thought were younger remains, the dating fell apart.

A lot of the resistance came from paleontologists who thought they had better evidence against the meteor than they actually did. It seems they're pissed because a Berkeley physicist, Luis Alvarez, came up with a story that pissed over the prevailing wisdom.

Nothing is ever certain especially but the evidence certainly seems to favor the meteor story and it keeps getting stronger as time goes by.

What I find interesting is how fast Wikipedia is updated. In a not directly related entry about the hypothetical Shiva Crater this news has already been added tot he end of it. I would of expected Chicxulub to be updated.

So, a 30-odd thousand year period of hardship punctuated by a major impact event resulting in the extinction of 75% of all terrestrial species.

For perspective, 30 thousand years ago Homo Sapiens were sharing the planet with several competing hominid species still, had yet to colonize the Americas and probably numbered no more than a few hundred thousand globally.

For a more alarming perspective, we measure most major extinction events in tens of thousands to a few million years in length, except the current one which is unfolding in a span of centuries and decades.

While it is a nice study, the reality is that we've never found non-reworked non-avian dinosaur bones above the boundary marked by the impact. More confirmation is always nice, but its been known for a while, and it was pretty blazingly clear. Some people don't -like- the idea that an impact killed them off, but the evidence has been pretty incontrovertible.

If this were true there wouldn't be any debate going on in scientific circles about this. this sounds an awful lot like the nonexistent 'consensus' on climate change. Just because a theory has been popular for a very long time does not make it correct. Scientific theories are adjusted as more and better data is made available.

For a theory that's only 30 years old, it's in pretty good shape. You're right that consensus doesn't mean squat - what matters are the data.

At first it was just the iridium spike in the Gubbio rocks that pointed to an asteroid and plankton size change spanning the KT boundary. Then the volcano group said that iridium is found in some volcano outgassing so perhaps the volcanos did the dinosaurs in. Then someone found a similar iridium-laced sequence in the Netherlands. And then an iridium KT sequence showed up in Spain. Then the meteor group found that all the KT iridium was laced with an isotope that isn't terrestial. Then they found a crater. But the crater was in water which was weird because the KT clays all suggested a land-based crater. Then they found tsunami evidence. Then they found that tektite distribution patterns that were consistent with a Coriolis distribution. The tektites helped tighten down the dating. Then someone figured out that the debris generated by the Chixilub geology would mimic a land-based crater not an aquatic crater.

Throughout the entire process, the meteor group kept pointing out that no one had found dinosaur remains younger than the KT boundary. When someone found what they thought were younger remains, the dating fell apart.

A lot of the resistance came from paleontologists who thought they had better evidence against the meteor than they actually did. It seems they're pissed because a Berkeley physicist, Luis Alvarez, came up with a story that pissed over the prevailing wisdom.

Nothing is ever certain especially but the evidence certainly seems to favor the meteor story and it keeps getting stronger as time goes by.

It's not that there is evidence of a meteor strike. But why is this one different?

My question is how much of an impact on the earth's axis this would have?

Would it have caused it to tilt more or less to the 23 degrees it is now?

Playing around with the calculator 9e0r9iu5 linked to; for an iron asteroid at 17km/sec and a 45 impact angle the threshold for a potential half degree tilt is 2800km in diameter; that's nearly as large as the moon (3500km), slightly larger than Neptune's principal moon Triton, and absolutely dwarfs Ceres's 950 km. At 51km/sec (cometary speed vs asteroid speed, and with an icy projectile but otherwise unchanged) the minimum impactor size grows to 3700 km in diameter. In both cases significant fractions of the Earth are melted from the impact (~10 and 20%) and the length of the day could be greatly changed (by up to ~32 and 21 hours).

I plugged in some numbers for something of the size of the K/T impactor (15km diameter, 20km/s speed, 90 degree angle, dense rock composition) and in 1000km distance (about 621 miles for you non-metric people out there) you'll get this: First, you will get 3rd degree burns from the fireball/thermal radiation of the impact, second, shaken by a magnitude >10 earthquake, and, third, hit by the shockwave/air blast coming at you with a speed of 342 m/s (766 mph). Everything at this location will be covered by about a meter of ejecta from the impact.

Don't forget that the impact site is in the ocean and Tsunamis will be generated. Also, immense Hurricanes could be generated over the impact site.

Go play with the calculator and you could find out what it takes to destroy earth

Is there one covering the resulting volcanic eruptions resulting from a large mass hitting the earth?

I plugged in some numbers for something of the size of the K/T impactor (15km diameter, 20km/s speed, 90 degree angle, dense rock composition) and in 1000km distance (about 621 miles for you non-metric people out there) you'll get this: First, you will get 3rd degree burns from the fireball/thermal radiation of the impact, second, shaken by a magnitude >10 earthquake, and, third, hit by the shockwave/air blast coming at you with a speed of 342 m/s (766 mph). Everything at this location will be covered by about a meter of ejecta from the impact.

Don't forget that the impact site is in the ocean and Tsunamis will be generated. Also, immense Hurricanes could be generated over the impact site.

Go play with the calculator and you could find out what it takes to destroy earth

That was fun modeling the consequences of the moon falling out of orbit and impacting the earth. Don't anyone plan on surviving.

While it is a nice study, the reality is that we've never found non-reworked non-avian dinosaur bones above the boundary marked by the impact. More confirmation is always nice, but its been known for a while, and it was pretty blazingly clear. Some people don't -like- the idea that an impact killed them off, but the evidence has been pretty incontrovertible.

If this were true there wouldn't be any debate going on in scientific circles about this. this sounds an awful lot like the nonexistent 'consensus' on climate change. Just because a theory has been popular for a very long time does not make it correct. Scientific theories are adjusted as more and better data is made available.

For a theory that's only 30 years old, it's in pretty good shape. You're right that consensus doesn't mean squat - what matters are the data.

....

You are wrong that consensus doesn't mean squat. Data is what matters to competent *experts*; to non-experts, including just about everyone here, what matters is the consensus among the experts. The only way the public, government etc. can know what science has determined is the most likely theory, is by looking for consensus among the experts. There isn't any other better way, certainly not the denialist's approach of intentional selection bias (i.e. cherry picking the few outlier experts that agree with them).

Telling the people who aren't experts to look directly to the data, which they are not capable of interpreting competently, instead of the consensus of the people who understand it, is a favorite trick of denialists to introduce false controversy, and obscure the real difference between those who know what they are talking about and those who don't. My grandmother's doubts about the data don't count as a valid counterpoint to the consensus of the climate science community.

Everyone has the right to look at the data, and everyone has the right to form an opinion, but only a fool takes that to mean that their uninformed (relatively) opinion is more valuable than the consensus of experts.